1. Field of the Invention
The present invention relates to a heat treatment apparatus and a heat treatment method.
2. Description of the Related Art
Heat treatment apparatuses have been used in fabrication of, e.g., semiconductor devices. These heat treatment apparatuses include horizontal type apparatuses and vertical type apparatuses. A large number of objects subjected to a treatment, e.g., a large number of wafers or a wafer are placed in columns or a column in a process tube constituting a heat treatment apparatus. A predetermined heat treatment is performed for wafers by using a cylindrical heater arranged surrounding the process tube. In this case, in order to perform a uniform heat treatment for the surfaces of the individual wafers located at different positions in the process tube, a uniform heating area having a uniform temperature distribution is required to be formed inside the process tube. Two or three temperature sensors are arranged at different positions inside the process tube in a conventional heat treatment apparatus. Outputs from these temperature sensors are compared with desired output values from temperature sensors which are obtained when a predetermined uniform heating area is formed inside the process tube. Heating is controlled by using a computer so that the actual output values from the temperature sensors come close to the predetermined ideal output values.
The temperature sensors are fixed at predetermined positions inside the process tube. For this reason, the temperatures estimated by the temperature sensors are not as actually measured temperatures but as empirically predicted temperatures obtained from the indicating values of temperature sensors, thereby performing temperature control in the process tube by a heater.
As a result of various experiments, it is confirmed that temperature differences between the temperature sensors greatly influence an desired uniform heating area in the process tube. In particular, when the packing density of semiconductor devices is increased and their manufacturing process becomes complicated, this tendency becomes conspicuous.